Digital Imaging Principle and Production Process II

2 Digital Photographic Imaging Principles and Applications

The front of the digital camera is equipped with optical lenses, framing frames, and quick-release parts. The operation method is similar to that of traditional cameras. The biggest difference is that the digital camera is equipped with an opto-electronic charge-coupled switching device CCD. When shooting an image, the optical lens is used to focus the scene on the CCD. Under light irradiation, the CCD pixel generates a current due to a change in the charge distribution, and the stronger the light, the greater the current. The binary code (image code) that converts the current to “0” or “1” is stored in the memory. This corresponds to the exposure process in a conventional camera. In order to produce a color image, the light is passed through a set of red, green, and green lights. The blue filter is then dropped onto the CCD pixels, and the signal is composited to produce a color image. Obviously, the greater the number of CCD pixels, the higher the resolution of the image and the larger the storage space occupied by each image. In fact, because each image occupies a large storage space (usually each image is hundreds of KB to MB), so many digital cameras compress the image information and store it on an onboard memory stick.

The next step is to transfer the image from the digital camera to a computer for editing. After the user is satisfied, he goes to the printer to print, and finally obtains a beautiful image (a digital image can produce a large image).

2.1 CCD photoelectric charge coupled conversion device

CCD is the optoelectronic charge coupled conversion device, which is developed on the basis of metal oxide-semiconductor devices. It has now become a very mature solid-state image sensor. In addition to capture processing and image sensing, CCDs can also be used for information processing and information storage, image analysis and processing. The two-dimensional CCDs produced by optical companies are mainly used for stationary electrophotography. The Kodak company has developed:

2.1.1 Full Frame CCD Image Sensor

The CCD sensor consists of a number of identical basic cells (pixels). Each pixel has a photosensitive area and a storage area. The photosensitive area generates photoelectrons, the accumulated charge is transferred to the storage area, and then output through the shift memory.

The full-frame CCD is an image capture device that combines a light-sensing unit with a memory unit. Its image capture process is divided into two parts, namely integration and readout. In the integration region, the photon-generated electrons accumulate in the image-forming unit. The number of electrons accumulated in each CCD pixel corresponds to the illumination of the image. The charge accumulated in each pixel in the read-out region is transferred to the output circuit. Such a CCD is simple to make, easy to use, and small in signal, but it cannot see light when read out. Therefore, a mechanical shutter is used in the camera, and the blue spectral response is also low.

A color image sensor can be formed by adding a color filter to each pixel of the sensor. The dye filter array produced by this photographic method is called a CFA because the human eye is most sensitive to the green part, so the CFA feels The number of green cells is twice that of red and blue cells.

When the illuminance is too large, when the charge generated in the pixel exceeds the capacity of the pixel, the excess charge will be strung into adjacent pixels, resulting in image blurring, and the function of lateral overflow (COD) is to charge excess charge before the charge is saturated. Vent.

The CCDs used in amateur still photography are equipped with COD because the scene conditions cannot be controlled. Cameras used in industry and science where the photographic conditions are controllable do not carry COD. Its high sensitivity and large pixel capacity.

2.1.2 6.4M Pixel Image Sensor

Kodak's professional digital camera DCS200C uses a 1029×1526 sequential scan CCD to capture images, an internal hard disk drive stores images, and a megapixel electronic camera outputs a color hard disk, which far exceeds the level of still camera cameras.

A rotating filter wheel is placed in front of the camera lens so that the CCD sensor sequentially receives red, green, and blue images so that only one single-color CCD can capture color images. Such a color sequential capture method has high resolution and color reproduction. it is good. However, due to vibration and other reasons, the camera and the subject are relative motion. When red, green, and blue images form an image, misregistration may occur. Therefore, it is only suitable for shooting still subjects.

The best capture LR for still photographic images is a full-frame CCD. The advantage of the full frame structure is the high occupancy of sequential scans, low noise, wide dynamic range, and high pixel density.

Shooting or scanning an image into the computer's image can be processed with the corresponding image processing software. Processing images on the Windows platform is very convenient. Because the image processing software opened under the platform has many varieties and functions, it can carry out various processing and processing that people can think of. If you want to make the slides to the photo image quality level, make it colorful, beautiful images, and extraordinary results, Adobe Photoshop software is currently the best choice. Photoshop software is one of the world's first developed image software, with features such as powerful and easy to operate. The software can at least process and trim image files.

2.2.1 Brightness and Contrast Adjustment: The brightness and contrast of the whole or partial image can be adjusted arbitrarily to show the effects of different image effects and traditional techniques.

2.2.2 Color Adjustment: The color level can be adjusted to remove unnecessary colors, and the color cast and saturation can be intuitively adjusted and corrected, and the positive and negative images can be converted to each other easily.

2.2.3 Eliminating fog, specks, and red-eye: Using image processing software can easily eliminate artifacts on the screen and adjust image sharpness.

2.2.4 Change the image texture: Make the image produce various deformations, so as to obtain an extraordinary and unique innovative art image. There are many deformed formats, such as: displacement - to make the image pixels in different directions Displacement, Pinch - press the image inwards or outwards, Polar coordinates - change the image coordinates from rectangular coordinates to polar coordinates or polar coordinates to rectangular coordinates. Square objects become circular, three-dimensional characters or objects produce bulging effects and so on.

2.2.5 Produce a variety of painting styles: The image can be processed to get different styles of painting effects, mainly soft effects (diffuse) - so that the image becomes like through the matte glass blur effect (make the picture rich Poetic); emboss—embossed or concave embossed objects on an image background; embossed effects—convert images into a series of three-dimensional cubes or pyramids. To change the image or generate a special 3D background, the size and height of the cubes or cones can be artificially selected; the “finded”—makes the image look like it is outlined by a pencil; the tiles effect (tiles) ) - The image is processed into blocks mosaic effect; Wind (wind) - Increase the effect of some small horizontal lines to generate wind, wind direction, wind effect can be made to choose; pointillize effect (pointillize) - an image Divide into random points to produce an effect that resembles a pointillist work; mezzotint--to generate a gravure intaglio image that brings the original image closest to one another; Fragmentation--makes the image unfocused Used for the rapid formation of focus background of the above kind can be attached to the catching protrusion like kind.

2.2.6 Miscellaneous: For example, simulate the shooting effect of various substances and simulate the processing effects of traditional darkroom techniques. (to be continued)